Abstract

We report our attempts to increase ethanol production from Zymomonas mobilis PTCC 1718, by optimization of the components of growth medium and culture conditions. First, low cost substrates, carbon and nitrogen sources, temperature and initial pH were optimized by one-factor-at-a-time method. Then, nutritional improvement was performed using Taguchi method. Amongst the different selected sources, sucrose and wheat bran have significant effects on ethanol production. The optimum temperature, inoculum-size and pH were 50°C, 12% (v/v) and 5.5, respectively. The optimal concentrations of nutritional components for improved ethanol production were 2.5 g/L sucrose, 1.5 g/L whey, 0.25 g/L wheat bran extract, 0.5 g/L yeast extract, 0.25 g/L peptone, 0.7 g/L KH₂PO₄ , 0.1 g/L (NH₄)₂SO₄ and 0.05 g/L MgSO₄. Ethanol production, which was 14.49 g/L (w/v) in the basal medium, increased to 41.67 g/L (w/v) and 86.26 g/L (v/v); about 2.8 and 5.9-fold higher than that in the basal medium, after optimization with one-factor-at-a-time and Taguchi method, respectively. Bioreactor fermentation was carried out in a 15 L stirred fermentor under optimal condition. Maximum ethanol production in 15 L fermentor indicated 91.22 g/L (w/v), about 6.3  fold higher than the basal medium.

Key words: Ethanol, medium components, Zymomonas mobilis PTCC 1718, optimization, Taguchi method.